Frank r



NlTED STATES ATENT Eric.

' FRANK R. coLvm, on NEW YORK, N. Y.

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 536,920, dated April 2,1895. Application filed December 20, 1894. Serial No. 532,388- (Nomodel-l To aZZ whom it may concern- Be it known that I, FRANK R. COLVIN,a CllllZBIl of the United States, residing in the city, county, andState of New York, have invented certain new and useful Improvements nTelephone Systems, of which the following 1s a specification.

This invention relates to telephone systems,

the object being to provide a simple and effective exchange system forinterconnecting a plurality of subscribers whose instruments are locatedin dilferent circuits, and for operating the system by batteries orelectric generators located only at the central station.

In carrying out my invention I provide a number of independent circuits,preferably metallic circuits, containing the several subscribersinstruments and extending from the outlying stations to the centraloffice, the several subscribers having a call-receiving apparatusnormally included in their circuits, the central office being providedwith a calling generator adapted to be out into the circuits.

At the central station is located a normally completed ground containingan electric generator and an indicator or annunciator for each circuit,a normally open ground with a circuit-closer beingprovided at theseveral subscribers stations so that upon operation of thecircuit-closer the indicator or annunciator at the central station willbe actuated. Each circuit terminates at the central station in a contactdevice by which a conducting cord provided with suitable plugs may beused to connect in series relation two subscribers desiringinter-communication. Interposed between the plugs is a battery or otherdirect current generator by which, when a connection between twocircuits is established, current is thrown over the line to renderoperative the talking instruments of the inter-communicatingsubscribers. At central station is also provided a listening or talkingcircuit having normally completed contacts with a plug by whichcommunication may be established with anyoutlying subscriber. A switchis also provided by which the listening circuit may be out out and amagneto or other calling generator thrown into circuit with the plug sothat any desired subscriber may be called up.

The several features of novelty of the inven tion will be moreparticularly hereinafter described, and will be definitely indicated inthe claims appended to this specification.

In the accompanying drawing whichillustrates my invention is showndiagrammatically asystem embodying my improvements. 1, 2 and 3 representa plurality of circuits connecting a number ofoutlying stations with acommon station located preferably at some central point. Each of thesecircuits may contain one or a plurality of instruments as may bedesired. In the circuit 1 a single subscribers station is interpolated,which is therefore a private line. In the circuit 2 two subscribersstations are interpolated, the circuit thus being shared by twostations. Each of the circuits terminates at the central station in aswitch 4, 4 4. comprising preferably two contacts normally held inengagement by a spring but adapted to be forced apart by a plug 5carrying two contact plates or surfaces of metal which engage the twocontacts.

A convenient organization comprises for the switch 4 a metallic post anda spring normally bearing against the same, the plug 5 comprising acentral metallic socket adapted to be forced over the pin and formcontact with the same and an insulated outer tube adapted to engage thespring. Thus, when the plug is inserted over the pin, the two concentricmetallic surfaces engage the two contact points of the switch. The twoparts of the plug connect with flexible conductors which lead to anothersimilarly constructed plug 5, a continuous current generator 6beingincluded in one of the conductors.

In a normally closed ground 7 at the central station is contained asignaling battery or other suitable generator 8, annunciators or otherindicators 9, 9, 9 connecting in multiple with this ground and with theseveral subscribers circuits. At each subscribers station is provided anormally open ground 10, 10*, 10*, 10 containing a circuit-closing key11, &c., by which a ground circuit may be completed through therespective annunciators or indicators at the central station and thusgive an indication that communication is desired with some othersubscriber.

Since a common generator 8 is provided for the several indicators 9, 9 9and the latter therefore grouped in multiple-arc relation to thegenerator, the generator 6 is connected in that branch of the doubleconducting cord which will be disconnected from the indicator brancheswhen the plug is inserted in the switch. For example, theindicatorbranches are shown in the diagram as connected with the springcontact of the respective switches and the battery 6 is in circuit withthe socket which forms a connection with the other contact. It isevident therefore that when two circuits are connected a short circuitwill not be afforded through the indicators 9, 9, and the latter may bemade of low resistance.

At each subscribers station is provided a call-receiving instrument 12,12, &c., which may be of any suitable character, but is preferably amagneto bell. This call-receiving instrumentis normallyincludedincircuit but is adapted to be cut outof circuit by shifting the telephonehook 13, the circuit then being completed by a normally open contactleading through the subscribers talking outfit as indicated. This hookis preferably of the character described in a former patent issued tome, No. 517,263, dated March 27, 1894, and is adapted when in its normalposition to sup port a telephone, but when thrown by a positive actionof the subscriber to the talking contact to be tilted to such a positionthat the telephone will not be supported by the hook. At the centralofiice is also provided a listening circuit 14 provided with a batteryand having a normally completed connection with a plug 15, similar tothe plugs 5 5, hereinbefore described. Thus, when the plug 15 is appliedto the jack switch corresponding to any subscriber, the central stationoperator will be placed in a position to talk with any subscriber.

In normally open relation to the switch contacts 16 16, connectingwith'the plug 15 is an electric generator 17, preferably a magnetogenerator, so that when the double key or switch 18 is actuated thelistening circuit 14 will be disconnected and the generator 17 connectedwith the terminals of the plug 15. Thus by inserting the plug 15 in anysubscribers switch and then shifting the switch 18 an operation of themagneto generator 17 will send suitable currents over the subscriberscircuit to actuate his bell 12 and call him up.

I preferably use as a talking instrument a battery transmitterof thecharacter described in a patent issued to me, No. 513,305, dated January23, 1894, in which a source of direct current exists on the talkingcircuit continuously during conversation, the conversation beingmaintained by a variation of resistance by the action of thetransmitter. Thus both transmitters and both receivers of the twocommunicating subscribers are in series relation during conversation. Itis evident, therefore, that a single battery, such as 6, for each pairof connecting cords may be used at the central station and that nobattery whatever need be employed at the subscribers stations. Asubscriber, however, is able to send in a call over a grounded circuit,one end of which is normally closed at the central station through abattery and indicator, and the other end of which is open at hisstation. Moreover, all subscribers are furnished with talking currentsby central station batteries. It is evident, therefore, that since nobattery is employed at the outlying stations the listening circuit 14 ofthe central station operator should also be provided with a battery asindicated. It is evident also that since the subscribers bells are notin the grounded circuit a call sent to central office by one of two ormore subscribers on the same circuit will not operate any subscribersbell, which can only be actuated by the central office operator. A

The subscribers bells should be of low inductance when more than one isemployed in series on the same circuit, since in such cases one or morewill be in the talking circuit.

The several subscribers circuits are preferably metallic circuits thoughsome features of the invention are applicable also to cases in whichgrounded talking circuits might be employed.

Some features of the invention will also prove of value in magnetotelephone systems where no batteries, so far as the talking circuit isconcerned, are employed; such a feature, for example, as the normallyopen ground at the outlying station and the co-opcrating call-receivingapparatus at the central station. Where two or more subscribers arelocated on the same circuit, as, for instance, on circuit 2, they arepreferably connected in series relation to the circuit. The bells beingof low inductance will not materially interfere with successfultelephonic transmission.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is

1. A telephone system comprising a plurality of outlying subscribersstations, at plurality of metallic circuits containing the telephonereceivers and direct current transmitters of the several subscribersleading to a central station, connectors at the central stationincluding a source of continuous current for connecting any two metalliccircuits and charging the transmitters, a calling generator at thecentral station, call-receiving instruments at the several stations, anormally completed ground including indicators for the several circuitsand a source of continuous current at the central station, and normallyopen grounds including a circuit-closer at the several stations.

2. A telephone system comprising a plurality of outlying subscribersstations, a plurality of metallic circuits containing the telephonereceivers and direct current transmitters of the several subscribersleading to a central station, a normally completed ground at centralstation for the several circuits including an indicator and battery, anormally transmitter and telephone receiver adapted I 5 to be cut in ateach subscribers station, connectors at the common station for couplingtwo subscribers circuits in series relation to each other, and a sourceof continuous current between said connectors for charging thetransmitters.

In testimony whereof I have hereunto subscribed my name this 18th day ofDecember,

FRANK R. OOLVIN. Witnesses:

RoBT. H. READ, G. W. GRAHAM.

